// tutorial01.c
// Code based on a tutorial by Martin Bohme (boehme@inb.uni-luebeckREMOVETHIS.de)
// Tested on Gentoo, CVS version 5/01/07 compiled with GCC 4.1.1

// A small sample program that shows how to use libavformat and libavcodec to
// read video from a file.
//
// Use
//
// 
//gcc -o tutorial01 tutorial01.c -lavutil -lavformat -lavcodec -lz -lavutil -lm -lpthread -lswscale
//
// to build (assuming libavformat and libavcodec are correctly installed
// your system).
//
// Run using
//
// tutorial01 myvideofile.mpg
//
// to write the first five frames from "myvideofile.mpg" to disk in PPM
// format.

#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libswscale/swscale.h> 

#include <stdio.h>
int img_convert(AVPicture *dst, int dst_pix_fmt,  
                const AVPicture *src, int src_pix_fmt,  
                int src_width, int src_height)  
{  
    int w;  
    int h;  
    static struct SwsContext *pSwsCtx;  

  
    w = src_width;  
    h = src_height;  
    pSwsCtx = sws_getContext(w, h, src_pix_fmt,  
                            w, h, dst_pix_fmt,  
                            SWS_BICUBIC, NULL, NULL, NULL);  
  
    sws_scale(pSwsCtx, (const uint8_t* const*)src->data, src->linesize,  
            0, h, dst->data, dst->linesize);  
 
 
    return 0;  
}  


void SaveFrame(AVFrame *pFrame, int width, int height, int iFrame) {
  FILE *pFile;
  char szFilename[32];
  int  y;
  
  // Open file
  sprintf(szFilename, "frame%d.ppm", iFrame);
  pFile=fopen(szFilename, "wb");
  if(pFile==NULL)
    return;
  
  // Write header
  fprintf(pFile, "P6\n%d %d\n255\n", width, height);
  
  // Write pixel data
  for(y=0; y<height; y++)
    fwrite(pFrame->data[0]+y*pFrame->linesize[0], 1, width*3, pFile);
  
  // Close file
  fclose(pFile);
}

int main(int argc, char *argv[]) 
{
	AVFormatContext *pFormatCtx;
	int             i, videoStream;
	AVCodecContext  *pCodecCtx;
	AVCodec         *pCodec;
	AVFrame         *pFrame; 
	AVFrame         *pFrameRGB;
	AVPacket        packet;
	int             frameFinished;
	int             numBytes;
	uint8_t         *buffer;

	if(argc < 2) 
	{
		printf("Please provide a movie file\n");
		return -1;
	}
	// Register all formats and codecs
	av_register_all();

	// Open video file
	pFormatCtx = avformat_alloc_context();
	if(avformat_open_input(&pFormatCtx, argv[1], NULL, NULL)!=0)
		return -1; // Couldn't open file

	// Retrieve stream information
	if(av_find_stream_info(pFormatCtx)<0)
		return -1; // Couldn't find stream information

	// Dump information about file onto standard error
	av_dump_format(pFormatCtx, 0, argv[1], 0);

	// Find the first video stream
	videoStream=-1;
	for(i=0; i<pFormatCtx->nb_streams; i++)
	if(pFormatCtx->streams[i]->codec->codec_type==AVMEDIA_TYPE_VIDEO) 
	{
		videoStream=i;
		break;
	}
	if(videoStream==-1)
		return -1; // Didn't find a video stream

	// Get a pointer to the codec context for the video stream
	pCodecCtx=pFormatCtx->streams[videoStream]->codec;

	// Find the decoder for the video stream
	pCodec=avcodec_find_decoder(pCodecCtx->codec_id);
	if(pCodec==NULL) 
	{
		fprintf(stderr, "Unsupported codec!\n");
		return -1; // Codec not found
	}
	// Open codec
	if(avcodec_open(pCodecCtx, pCodec)<0)
		return -1; // Could not open codec

	// Allocate video frame
	pFrame=avcodec_alloc_frame();

	// Allocate an AVFrame structure
	pFrameRGB=avcodec_alloc_frame();
	if(pFrameRGB==NULL)
		return -1;

	// Determine required buffer size and allocate buffer
	numBytes=avpicture_get_size(PIX_FMT_RGB24, pCodecCtx->width,
	pCodecCtx->height);
	buffer=(uint8_t *)av_malloc(numBytes*sizeof(uint8_t));

	// Assign appropriate parts of buffer to image planes in pFrameRGB
	// Note that pFrameRGB is an AVFrame, but AVFrame is a superset
	// of AVPicture
	avpicture_fill((AVPicture *)pFrameRGB, buffer, PIX_FMT_RGB24,
	pCodecCtx->width, pCodecCtx->height);
  
	// Read frames and save first five frames to disk
	i=0;
	while(av_read_frame(pFormatCtx, &packet)>=0) 
	{
		// Is this a packet from the video stream?
		if(packet.stream_index==videoStream) 
		{			
			// Decode video frame
			avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);
	      
			// Did we get a video frame?
			if(frameFinished) 
			{
				// Convert the image from its native format to RGB
				img_convert((AVPicture *)pFrameRGB, PIX_FMT_RGB24, 
				(AVPicture*)pFrame, pCodecCtx->pix_fmt, pCodecCtx->width, 
				pCodecCtx->height);

				// Save the frame to disk
				if(++i<=5)
				{
					SaveFrame(pFrameRGB, pCodecCtx->width, pCodecCtx->height,i);
				}
				else
				{
					break;
				}
			}
    	}  
	    // Free the packet that was allocated by av_read_frame
	    av_free_packet(&packet);
	}

	// Free the RGB image
	av_free(buffer);
	av_free(pFrameRGB);

	// Free the YUV frame
	av_free(pFrame);

	// Close the codec
	avcodec_close(pCodecCtx);

	// Close the video file
	av_close_input_file(pFormatCtx);

	return 0;
}
